1. Field of the Invention
The present invention relates to a wireless local loop system, and more particularly, to an improved data transmission/reception apparatus for a WLL system using a CDMA method.
2. Description of the Background Art
In general, a wireless local loop (hereinafter, xe2x80x9cWLLxe2x80x9d) system employs a wireless communication network instead of wired network, between subscribers"" terminals and a telephone company and enables data communication, i.e., internet, as well as voice communication using traffic channels.
FIG. 1 is a schematic block diagram illustrating a general WLL system. As shown therein, the system includes voice purpose or data purpose terminals 10, a subscriber"" radio interface unit 20 interfaced to the terminals 10, a base station 30 for wireless data reception/transmission with the subscriber""s radio interface unit 20, a base station controller 40 for controlling the base station 30, and a WLL switching center 50 for forming a wired communication pathway to enable a voice or data communication for example through internet via PSTN (Public Switched Telephone Network) or PSPDN (Public Switched Packet Data Network).
More specifically, the subscriber""s radio interface unit 20 performs a wireless interface between the base station 30 and the subscriber""s terminal 10 and it is connected to a telephone set, facsimile machine or computer through an analog or digital data path so as to enable voice and data service.
The base station 30 is interfaced to the base station controller 40 and it is interfaced through wireless channel to the subscriber""s radio interface unit 20 so as to form a data path from the base station controller 40 to the subscriber""s radio interface unit 20.
The base station controller 40 performs major roles of the WLL system such as a call processing for a reception/transmission signal, base station management and voice signal compression. The WLL switching center 50 serves to interface telephone network or data network (PSTN/PSPDN) with wireless subscribers"" network.
FIGS. 2 and 3 specifically illustrate the subscriber""s radio interface unit 20 and the base station 30, wherein the two apparatuses 20, 30 carry out similar performance with similar construction.
First, as shown in FIG. 2, the subscriber""s radio interface unit 20 includes a duplexer 21 for switching transmission/reception signals, an RF receiver 22 for down-converting the signal from the duplexer 21, a demodulator 23 for demodulating the down-converted signal, a decoder 24 for decoding the demodulated signal, a vocoder 29 connected to a voice class terminal and for encoding a voice signal, a DPU (Data Port Unit) 28 serving as a terminal connection apparatus for data, an encoder 27 for performing a convolutional coding with regard to a voice signal or data signal from the DPU 28 or the vocoder 29, a modulator 26 for modulating the encoded signal, and an RF transmitter 25 for up-converting the modulating signal.
The RF receiver 22 includes a BPF (Band Pass Filter) 22-1 for filtering a signal received through the duplexer 21, a LNA (Low Noise Amplifier) 22-2 for amplifying the filtered signal into low noise, and a down converter 22-3 for down-converting the amplified signal into a low pass band signal.
Also, the RF transmitter 25 includes an up converter 25-1 for up-converting the signal from the modulator 26 into a high frequency signal, a PA (Power Amplifier) 25-2 for amplifying the frequency-converted signal to a predetermined level, and a BPF 25-3 for filtering the amplified signal.
As further shown in FIG. 3, the base station 30 is similar in construction and operation to the subscriber""s radio interface unit 20 in FIG. 2 and its description will be omitted, accordingly.
With reference to FIGS. 1 through 3, the conventional voice or data transmission/reception steps for a WLL system will now be described.
Initially, according to the data transmission steps from a subscriber""s side, the voice signal from a voice class terminal such as a telephone set is converted to a PCM (Pulse Code Modulation) signal through a vocoder 29 and applied to the encoder 27 through the PCM bus. The data signal from the data-purposed terminal such as a PC (personal computer) is applied to the encoder 27 through the DPU 28.
Then, the encoder 27 converts the applied PCM signal to a convolutional code, and the converted signal is modulated by the modulator 26 and applied to the RF transmitter 25. The applied signal is converted to a high frequency signal by the up converter 25-1 and amplified to a predetermined power level demanded through the PA 25-2 and it is also filtered through the BPF 25-2 and transmitted into a free space.
The base station receives the data from the subscriber"" side according to the aforementioned steps and its wireless communication steps will now be explained.
The signal received via the antenna through the free space is applied through the duplexer 31 to the RF receiver 32, and the RF receiver 32 filters the signal received through the duplexer 31 and amplifies the filtered signal to the LNA, thereby down-converting the amplified signal to a low pass band signal.
The down-converted signal is demodulated by the demodulator 33 and decoded by the decoder 34. Then, the voice signal passes through the PSTN and the data signal passes through the PSPDN, thereby enabling the subscriber to perform data communication with another subscriber or internet network. Those steps are similarly carried out when transmitting data from a base station to a subscriber.
The conventional WLL system employs a circuit switching method to implement the transmission/reception of voice or data. According to the circuit switching method, when an exchanger starts interfacing from a signal-transmitting terminal, a channel to a signal-receiving terminal is determined and the channel is seized until the communication is terminated, thereby transmitting/receiving communication information. For example, a telephone network follows the circuit switching method.
FIG. 4 is a flow chart schematically illustrating data transmitting/receiving steps in the conventional WLL system. As shown therein, the base station determines whether a hook off/on signal is output from a subscriber""s terminal for notifying a communication start/end in step Si. When the hook off signal notifying a communication start is transmitted, it is identified whether there is an unoccupied channel in step S2. When all the channels are in use, a busy tone is generated and transmitted to the terminal in step S3 and when there are unoccupied channels, one of the unoccupied channels is assigned in step S4.
Then, in step S5 the terminal serves to transmit voice or data through the assigned channel, wherein the assigned channel remains seized until the voice or data communication is terminated, that is, until the hook on signal is sensed.
The thusly operating conventional WLL system permits simultaneously communicable multiple channels to be assigned to a single base station. The respective base stations form wireless communication channels between subscribers using down-converting and up-converting different frequencies through a plurality of limited channels.
The subscribers-housing capacity per base station in the conventional WLL system is presumed to range 10 times as large as the wireless channel number. Here, the subscribers include telephone subscribers using voice communication, fix subscribers, and data communication subscribers interfaced to personal computers and work stations for internet or data communication.
The reason why the subscribers capacity is assumed to be ten times as large as the channel number is that voice communication subscribers generally terminate the communication within 3 minutes according to local statistics in South Korea.
In the WLL system performing a data communication as well as a voice communication, if the concentration is set on the basis of voice communication time period to include data communication subscribers, there may inevitably occur communication circuit shortage. In case of data communication, the communication time period is significantly long, compared to the voice communication.
Also, in case of data communication, the data transmitting/receiving time period which is practically taken to terminate the data communication from the start of interfacing is relatively short so that a channel-seizing method may disadvantageously leave some channels unused due to the channel seizure from start to end.
The present invention is directed to overcoming disadvantages of the conventional WLL system.
Therefore, it is an object of the present invention to provide a data transmission/reception method for a WLL system wherein a data exclusive channel is assigned for common use of multiple subscribers and the data communication is implemented through the data communication channel using a packet exchange method.
To achieve the above-described object, there is provided a WLL (wireless local loop) system using a CDMA (code division multiple access) method according to the present invention which includes a data transmitter, a data receiver, a data transmission/reception buffer, and a controller. The system implements a voice and data communication including the steps of performing a voice communication through a plurality of voice communication channels assigned to respective subscribers by a circuit switching method during a transmission/reception of the voice signal, and performing a data communication by a packet switching method in a way in which a plurality of subscribers share in common predetermined data communication channels during the transmission/reception of the data signal.
The features and advantages of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific example, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.